There are few ingredients in this toast, barely touched, so every one of them matters and should be the best you can find. Be sure the avocado is firm-soft here, so that it just barely gives when squeezed.
Squeeze the lemon juice over the slices of avocado, then lay the slices of avocado over the hot toast. Drizzle the tahini over the avocado and the toast. Finish with the salt and sesame seeds. Eat immediately, then repeat.